Joseph DeVore's Blog: Flex Custom CheckBox Icons

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="vertical"
verticalAlign="middle"
backgroundColor="white">

<mx:Style>
CheckBox {
/* Unselected icons */
upIcon: Embed(source="assets/bullet_red.png");
overIcon: Embed(source="assets/bullet_red.png");
downIcon: Embed(source="assets/bullet_yellow.png");
/* Selected icons */
selectedUpIcon: Embed(source="assets/bullet_green.png");
selectedOverIcon: Embed(source="assets/bullet_green.png");
selectedDownIcon: Embed(source="assets/bullet_yellow.png");
}
</mx:Style>

<mx:CheckBox id="x1"
label="CheckBox Label Here..."
fontSize="10"
fontWeight="bold"/>
</mx:Application>